How to edit inset face after executing inset command
Select the vertices which compose edges and scale.  S
You probably know you can scale in two dimensions.  Lets assume XZ in
your model. 
SShift+Y
You probably know you can choose the center point of the scale if
necessary.  Moving the cursor to the bottom middle might be your style. Otherwise you might move the points in z direction.
Otherwise undo or delete your work and inset a second time